Method for fabricating liquid crystal display panel

ABSTRACT

A method for fabricating a liquid crystal display panel is provided. A thin film transistor array substrate and a color filter array substrate are formed. The thin film transistor array substrate includes a screen region having gate lines, data lines, thin film transistors, and pixel electrodes; a pad region having gate pads, an overetch prevention pattern formed overlapped with a gate insulating film in an outer portion of each gate pad, and data pads; data pad protection electrodes each on a respective data pad, and a protection film on an entire surface of the screen region and the pad region. The thin film transistor array substrate and the color filter array substrate are bonded together so that the pad region remains uncovered. Also, a portion of the protection film and the overetch prevention pattern of the pad region are etched to partially expose the gate pads and the data pad protection electrodes, and to form gate holes in the gate insulating film over corresponding gate pads.

This application is a divisional of U.S. patent application Ser. No.10/422,724, filed Apr. 25, 2003, which is hereby incorporated byreference. This application also claims the benefit of Korean PatentApplication No. P2002-43305 filed on Jul. 23, 2002, and Korean PatentApplication No. P2002-84910 filed on Dec. 27, 2002, which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid crystal display devices, andmore particularly, to a method for fabricating a liquid crystal displaypanel which can simplify a fabrication process.

2. Background of the Related Art

In keeping pace with development of an information oriented society,demands on display technologies have increased in a variety of aspects.Recently, to meet the demands, different flat display technologies, suchas Liquid Crystal Display (LCD) devices, Plasma Display Panel (PDP)devices, Electro Luminescent Display (ELD) devices, Vacuum FluorescentDisplay (VFD) devices, and the like, have been under development. Someof these technologies are employed as display devices in variousapplications. Among the flat displays, LCD devices have been the mostwidely used as portable displays. Here, LCD devices have been replacingthe CRT (Cathode Ray Tube) due to excellent picture quality, lightweight, thinness, and low power consumption. In addition to portable LCDdevices, such as monitors for notebook computers, LCD devices are underdevelopment for televisions and computer monitors.

Despite the various LCD technical developments on the LCD device for usein different fields, the efforts to enhance picture quality in LCDdevices have been inconsistent with respect to the features andadvantages of the LCD device in many aspects. Therefore, for employingthe LCD device in various fields as a general display device, it is keyto develop and implement high quality picture (such as high definition),high luminance, and large sized screen with light weight, thinness, andlow power consumption.

The LCD device includes a liquid crystal display panel for displaying apicture, and a driving portion for providing a driving signal to theliquid crystal panel. The liquid crystal display panel has upper andlower substrates bonded with a gap therebetween, and a liquid crystallayer formed between the upper and lower substrates. The lower substrate(a thin film transistor array substrate), has a plurality of gate linesand data lines arranged intersecting each other, thin film transistorsat every intersection of the gate lines and the data lines as switchdevices, pixel electrodes and the like formed in an liquid crystal cellunit each connected to the thin film transistors, and an alignment filmcoated over the system elements. The gate lines and data lines receivescan signals and pixel voltage signals from driving circuits throughrelevant pads respectively. A given thin film transistor supplies apixel voltage signal supplied to a data line to a pixel electrode inresponse to a scan signal supplied to a gate line. The upper substrate(a color filter array substrate) has color filters formed for each LCDcell, a black matrix for separating the color filters and reflection ofan external light, a common electrode for commonly supplying a referencevoltage to the LCD cells, and an alignment film coated thereon.

Fabrication of the LCD panel is finished by separately fabricating andbonding the thin film transistor array substrate and the color filterarray substrate followed by injecting liquid crystal therein and sealingthe substrates. In fabricating the LCD device, not one LCD panel isformed on one substrate, but rather a plurality of LCD panels are formedon a large sized substrate depending on the size of the substrate andthe LCD panel.

The thin film transistor (TFT) array substrate of the LCD panel is amajor portion of the cost of the LCD panel because the TFT arraysubstrate has a complicated fabrication process including semiconductorfabrication processes and a plurality of masking processes. For solvingthis, fabrication processes have been developed to reduce a number ofmask processes. This is because each mask process includes manyprocesses, such as deposition, cleaning, photolithography, etching,photoresist peeling, and inspection.

A related art method for fabricating an LCD panel will be described.First, the related art TFT array substrate in the LCD panel will bedescribed.

Referring to FIG. 1, on the lower substrate 20 (see FIGS. 2A-2D), thereare gate lines 21 running in one direction in parallel at fixedintervals, a gate electrode 21 a projected from the gate line 21 in onedirection, and a storage lower electrode (not shown) at a position of astorage capacitor of a forward gate line. A gate pad 21 b is disposed atan end of the gate line 21, and a data pad 26 c is disposed at an end ofthe data line 26. A gate insulating film is disposed on the lowersubstrate 20 having the gate line 21, the gate electrode 21 a, and thestorage lower electrode. An active layer 25 is disposed on the gateinsulating film over the gate electrode 21 a. The active layer 25 isformed of amorphous silicon. Data lines 26 are formed perpendicular tothe gate lines 21 to define pixel regions. A source electrode 26 aprojects from the data line 26 in one direction and overlaps with aportion of the active layer 25. A drain electrode 26 d overlaps with theother portion of the active layer 25 spaced from the source electrode 26a. An ohmic contact layer 24 a (see FIGS. 2C-2D) is disposed on theactive layer 25 under the source electrode 26 a and the drain electrode26 b. A storage upper electrode (not shown) is formed together with thedrain electrode 26 b extended to a top of the storage lower electrodeformed on the forward gate line. A pixel electrode 28 a contacts thestorage upper electrode and the drain electrode 26 b through respectivecontact holes in the pixel region. An organic film (not shown) is formedon an entire surface of the lower substrate 20 having the thin filmtransistor and the pixel region having contact holes to the gate pad 21b and data pad 26 c.

A related art method for fabricating a thin film transistor arraysubstrate of an LCD panel will be described. FIGS. 2A-2D illustratesections across lines I-I′, II-II′ and III-III′ in FIG. 1 showing thesteps of a fabrication method.

Referring to FIG. 2A, a conductive metal is deposited on the lowersubstrate 20 and patterned to form a gate pad 21 b having apredetermined large area at one end, a gate line extended in onedirection from the gate pad 21 b, and a gate electrode 21 a projected ina direction from the gate line. Then, an insulating film 22, and firstand second semiconductor layers (an amorphous silicon layer, and n⁺doped amorphous silicon layer) 23 and 24 for forming the active layerare formed on an entire surface of the lower substrate 20 having thegate electrode 21 a formed thereon in succession.

Next, referring to FIG. 2B, the first and second semiconductor layers 23and 24 of FIG. 2A are patterned by using a mask to form an active layer25 of an island form on the gate electrode 21 a.

Referring to FIG. 2C, a conductive metal is deposited on an entiresurface of the lower substrate having the active layer 25 formed thereonand patterned to form a plurality of data lines formed in a directionperpendicular to the gate lines. Each data line has a data pad 26 c atan end thereof, source electrode 26 a each projected from the data linein a side direction at the gate electrode 21 a, and a drain electrode 26b spaced from the source electrode 26 a. In patterning the conductivemetal, an ohmic contact layer 24 a is formed due to over-etching of thesecond semiconductor layer 24 between the source electrode 26 a anddrain electrode 26 b. Then, a protection film 27 is formed on an entiresurface of the lower substrate 20 inclusive of the drain electrode 26 b.

Next, referring to FIG. 2D, the protection film 27 is etched by aphoto-mask process to form first, second, and third contact holes 29 a,29 b, and 29 c to the drain electrode 26 b, the gate pad 21 b and thedata pad 26 c, respectively. Then, a transparent conductive metal isdeposited on the protection film 27 inclusive of the first, second,third contact holes 29 a, 29 b and 29 c, and patterned to form a pixelelectrode 28 a in the pixel region in contact with the drain electrode26 b through the first contact hole 29 a, a gate terminal 28 b on thesecond contact hole 29 b and the protection film 27 adjacent to thecontact hole 29 b in contact with the gate pad 21 b, and a data terminal28 c on the third contact hole 29 c and the protection film 27 adjacentto the third contact hole 29 c in contact with the data pad 26 c.

In above processes, five masks are used. In carrying out a pad openingprocess by forming the second and third contact holes 29 b and 29 c inthe first gate pad 21 b and data pad 26 c, since there are two layers ofthe gate insulating film 22 and the protection film 27 on the gate pad21 b and only one layer of the protection film 27 on the data pad 26 c,a defect is liable to occur due to a thickness difference in opening thepad. In other words, if etching is carried out until the data pad 26 cis exposed, the gate pad 21 b may not be opened. Thus, the use of fivemasks leads to a complicated fabrication process and a defective padopening.

Consequently, a four mask fabrication process is recently introduced toreduce the number of masks. A related art method for fabricating a TFTarray substrate in accordance with a four mask fabrication process willbe described. FIG. 3 illustrates an enlarged plan view of a pixel on aTFT array substrate according to related art LCD, and FIG. 4 illustratessections across lines I-I′, II-II′, and III-III′ in FIG. 3. FIGS. 5A-5Dillustrate sections showing the steps of a method for fabricating a TFTarray substrate shown in FIG. 4.

Referring to FIGS. 3 and 4, the TFT array substrate includes gate lines41 and data lines 45 formed on the lower substrate 40 to cross eachother with the gate insulating film 42 therebetween, a thin filmtransistor T formed an every intersection, a pixel electrode 49 a formedin a cell region defined by the crossing structure, a gate pad 41 bformed at an end of the gate line 41, and a data pad 46 at an end of thedata line 45. The thin film transistor T is provided with a gateelectrode 41 a projected from one side of the gate line 41, a sourceelectrode 45 a projected from one side of the data line 45, a drainelectrode 45 b partly projected from the source electrode 45 a and incontact with the pixel electrode 49 a, and an active layer 43 forming achannel between the source electrode 45 a and the drain electrode 45 b.The active layer 43 is formed overlapping with and under the data pad46, the data line 45, the source electrode 45 a, and the drain electrode45 b. The active layer 43 further includes a channel portion between thesource electrode 45 a and the drain electrode 45 b. The ohmic contactlayer 44 is disposed on the active layer 43 for ohmic contact with thedata pad 46, the data line 45, the source electrode 45 a, and the drainelectrode 45 b.

The thin film transistor T supplies a pixel voltage signal to the dataline 45 in response to the gate signal supplied to the gate line ischarged to the pixel electrode 49 a. The pixel electrode 49 a contactsthe drain electrode 45 b of the thin film transistor T through the firstcontact hole 48 a, which passes through the protection film 47. Thepixel electrode 49 a causes a potential difference with a commonelectrode on the upper substrate (not shown) due to the charged pixelelectrode. The potential difference causes the liquid crystal betweenthe thin transistor substrate and the upper substrate to rotate bydielectric anisotropy, to transmit a light incident thereto from a lightsource (not shown) through the pixel electrode 49 a toward the uppersubstrate.

The gate line 41 is connected to the gate driver (not shown) through thegate pad portion. The gate pad portion is provided with a gate pad 41 bextended from the gate line 41, and a gate pad terminal 49 b connectedto the gate pad 41 b through the second contact hole 48 b passed throughthe gate insulating film 42 and the protection film 47. The data line 45is connected to the data driver (not shown) through the data padportion. The data pad portion is provided with a data pad 46 extendedfrom the data line 45, and a pad terminal 49 c connected to the data pad46 through the third contact hole 48 c passed through the protectionfilm 47. The gate pad 41 b and data pad 46 are connected to a TCP outputpad (not shown) having a drive integrated circuit mounted thereonthrough an anisotropic conductive film.

A related art method for fabricating the foregoing TFT array substrateby using the four mask fabrication process will now be described indetail.

Referring to FIG. 5A, a gate metal layer is deposited on the lowersubstrate 40 by sputtering and the like, and patterned byphotolithography and etching using a first mask to form a gate line 41in one direction. A gate electrode 41 a is projected from one side ofthe gate line 41 and a gate pad 41 b at an end of the gate line 41. Thegate metal layer is a single layer of Cr, Mo, or Al or a double layer.

Referring to FIG. 5B, a gate insulating film 42, an active layer 44, anohmic contact layer 43, and data patterns are formed on the lowersubstrate 40 in succession inclusive of the gate patterns (gate line 41,gate electrode 41 a, and gate pad 41 b). Using the data portion, a datapad 46 is formed at the data pad portion. In more detail, a gateinsulating film 42, an amorphous silicon layer, an n⁺ amorphous siliconlayer, and data metal layer are formed in succession on the lowersubstrate 42 having gate patterns formed thereon by deposition, such asPECVD, or sputtering. A photoresist pattern is formed on a data metallayer with a second mask by photolithography. In this instance, arefractive exposure mask has a refractive exposure portion at a channelportion of the thin film transistor for making a height of thephotoresist pattern at the channel portion lower than other data patternpart. Then, a wet etching is carried out using the photoresist patternto form data patterns inclusive of the data line 45, the source line 45a, and the drain electrode 45 b integrated with the source electrode 45a. Then, a dry etching is carried out using the same photoresist patternto pattern the n⁺ amorphous silicon layer, and the amorphous siliconlayer at the same time to form an ohmic contact layer 44 and the activelayer 43. Next, the photoresist pattern having a relatively low heightin the channel portion is removed by ashing, and the data pattern andthe ohmic contact layer 44 are dry etched. Accordingly, the active layer43 in the channel portion is exposed to separate the source electrode 45a and the drain electrode 45 b. Then, the photoresist pattern left onthe data pattern portion is removed by stripping.

In the foregoing process, the photoresist pattern is formed in the datapad portion, and the data pad 46 having the amorphous silicon layer, then⁺ amorphous silicon layer, and the data metal layer stacked thereon isformed as the wet and dry etching are carried out. The gate insulatingfilm 42 is formed of an inorganic insulating material, such as siliconoxide SiOx, or silicon nitride SiNx. The data metal layer is formed ofMo, Ti, Ta, or an Mo alloy.

Referring to FIG. 5C, a protection film 47 is formed on an entiresurface of the lower substrate 40 inclusive of the data line 45 bydeposition, such as PECVD or the like, and etched with a third mask byphotolithography and etching to form a first to a third contact holes 48a, 48 b, and 48 c. The first contact hole 48 a is formed to pass throughthe protection film 47 and expose the drain electrode 45 b. The secondcontact hole 48 b is formed to pass through the protection film and thegate insulating film 42 and expose the gate pad 41 b. The third contacthole 48 c is formed to pass through the protection film 47 and exposethe data pad 46. The protection film 47 is formed of an inorganicinsulating material, the same as the gate insulating film 42, an acrylgroup organic compound of a low dielectric constant, or an organicinsulating material, such as BCB or PFCB, or the like.

Referring to FIG. 5D, transparent electrode patterns are formed on theprotection film 47. A transparent electrode material is deposited on anentire surface of the protection film 47 by deposition, such assputtering. Then, the transparent electrode material is patterned with afourth mask by photolithography and etching to form transparentelectrode patterns inclusive of the pixel electrode 49 a, the gate padterminal 49 b, and the data pad terminal 49 c. The pixel electrode 49 ais electrically connected to the drain electrode 45 b through the firstcontact hole 48 a. The gate terminal 49 b is electrically connected tothe gate pad 41 b through the second contact hole 48 b. The data padterminal 49 c is electrically connected to the data pad 46 through thethird contact hole 48 c.

Thus, in the related art TFT substrate and a method for fabricating thesame, the employment of a four mask process permits a reducedfabrication process and saves production cost proportionately thereto ascompared with the case of employing a five mask process. However, evenif the thin film transistor substrate is fabricated using the four maskprocess, a contact hole forming process is required for opening the gatepad and the data pad formed at ends of the gate line and data line.Moreover, in formation of the contact holes, like the five mask process,even if removal of only the protection film is required in a portionover the data pad, removal of two layers of the gate insulating film andthe protection film is required in a portion over the gate pad, therebycausing a defective pad opening. Thus, even if the fabrication processis simplified by reducing a number of masks, there is a problem of adefective opening in opening gate pad and data pad.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method forfabricating a liquid crystal display panel that substantially obviatesone or more of the problems due to limitations and disadvantages of therelated art.

An object of the present invention is to provide a method forfabricating a liquid crystal display panel which can simplify afabrication process and resolving a defective pad opening.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a methodfor fabricating a liquid crystal display panel comprises the steps offorming a thin film transistor array on a lower substrate, the thin filmtransistor array having gate lines, data lines, data pads, thin filmtransistors and pixel electrodes; forming a color filter array on anupper substrate; bonding the upper substrate and lower substratetogether; cutting the bonded upper and lower substrates into cells; andexposing the gate pads and the data pads at ends of the gate lines andthe data lines on the lower substrate of the bonded upper and lowersubstrates.

In another aspect, a method for fabricating a liquid crystal displaypanel comprises the steps of forming a thin film transistor arraysubstrate including a screen region having gate lines, data lines, thinfilm transistors, and pixel electrodes, a pad region having gate pads,an overetch prevention pattern formed overlapped with a gate insulatingfilm in an outer portion of each gate pad, and data pads, data padprotection electrodes each on a respective data pad, and a protectionfilm on an entire surface of the screen region and the pad region;forming a color filter array substrate; bonding the thin film transistorarray substrate and the color filter array substrate so that the padregion remains uncovered; etching a portion of the protection film andthe overetch prevention pattern of the pad region to partially exposethe gate pads and the data pad protection electrodes, and to form gateholes in the gate insulating film over corresponding gate pads.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 illustrates an enlarged plan view of a pixel on a thin filmtransistor array substrate in a related art liquid crystal displaypanel;

FIGS. 2A-2D illustrate sections across lines I-I′, II-II′ and III-III′in FIG. 1 showing the steps of a fabrication method;

FIG. 3 illustrates an enlarged plan view of a pixel on a TFT arraysubstrate in another related art LCD panel;

FIG. 4 illustrates sections across lines I-I′, II-II′, and III-III′ inFIG. 3;

FIGS. 5A-5D illustrate sections showing the steps of a method forfabricating a TFT array substrate shown in FIG. 4;

FIGS. 6A and 6B illustrate flow charts each showing the steps of amethod for fabricating a liquid crystal display panel in accordance withan exemplary embodiment of the present invention;

FIG. 7 illustrates an enlarged plan view of a pixel on a TFT arraysubstrate in accordance with a first exemplary embodiment of the presentinvention;

FIGS. 8A-8C illustrate sections across lines IV-IV′, V-V′, and VI-VI′ inFIG. 7 showing the steps of a fabrication method;

FIG. 9 illustrates a method for opening a gate pad in an LCD panel ofthe present invention;

FIGS. 10A and 10B illustrate before and after opening of a gate pad inaccordance with a first preferred embodiment of the present invention;

FIG. 11 illustrates a method for opening data pad in an LCD inaccordance with an exemplary embodiment of the present invention;

FIGS. 12A and 12B illustrate before and after opening of a data pad inaccordance with the first exemplary embodiment of the present invention;

FIG. 13 illustrates an enlarged plan view of a pixel on a TFT arraysubstrate in accordance with a second exemplary embodiment of thepresent invention;

FIGS. 14A-14D illustrate sections across lines IV-IV′, V-V′, and VI-VI′in FIG. 13 showing the steps of a fabrication method;

FIG. 15 illustrates an enlarged plan view of a pixel on a TFT arraysubstrate in accordance with a third exemplary embodiment of the presentinvention;

FIGS. 16A-16C illustrate sections across lines IV-IV′, V-V′, and VI-VI′in FIG. 13 showing the steps of a fabrication method;

FIG. 17A illustrates a section showing the step of bonding a TFT arraysubstrate and a color filter array substrate of an LCD panel inaccordance with the third exemplary embodiment of the present invention;and FIG. 17B illustrates a section showing the step of exposing a padportion in an LCD panel in accordance with the third exemplaryembodiment of the present invention;

FIG. 18 illustrates a section showing an overetch in opening a gate padand a data pad in accordance with the third exemplary embodiment of thepresent invention;

FIG. 19 illustrates a plan view of a TFT array substrate in an LCD panelin accordance with a fourth exemplary embodiment of the presentinvention;

FIG. 20 illustrates sections across lines VII-VII′, VIII-VIII′, andIX-IX′ in FIG. 19;

FIGS. 21A-21G illustrate sections across lines VII-VII′, VIII-VIII′, andIX-IX′ in FIG. 19 showing the steps of a fabrication method;

FIG. 22A illustrates a section showing the step of bonding a TFT arraysubstrate and a color filter array substrate of an LCD panel inaccordance with the fourth exemplary embodiment of the presentinvention; and

FIG. 22B illustrates a section showing the step of exposing a padportion in an LCD panel in accordance with the fourth exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIGS. 6A and 6B illustrate flow charts each showing the steps of amethod for fabricating a liquid crystal display panel in accordance withan exemplary embodiment of the present invention. The liquid crystaldisplay panel includes a lower substrate, an upper substrate, and aliquid crystal panel injected between the upper substrate and a lowersubstrate. The lower substrate has a plurality of gate lines arranged atfixed intervals and a plurality of data lines arranged at fixedintervals perpendicular to the gate lines formed thereon to form amatrix of pixel regions each with a thin film transistor and a pixelelectrode formed therein. The upper substrate has a black matrix layerand a color filter layer formed thereon.

A fabrication process of the LCD panel includes the steps of fabricatinga substrate, fabricating a cell, and fabricating a module. A gate padand a data pad are at ends of the gate line and the data line on thelower substrate. Referring to FIGS. 6A and 6B, the present inventionsuggests carrying out opening of the gate pad and the data pad, notduring fabrication of the lower substrate (the TFT array substrate), butafter bonding of the upper and lower substrates.

The substrate fabrication process includes a process for fabricating alower substrate (a TFT array substrate) (S10-1) of a glass substrate,and a process of fabricating an upper substrate (a color arraysubstrate) (S10-2) of a glass substrate. The process for fabricating alower substrate is a process for forming thin film transistor arrayinclusive of gate lines, data lines, thin film transistors, pixelelectrodes on the lower substrate. The process for fabricating an uppersubstrate is a process for forming a R(Red), G(Green) and B(Blue) colorfilter layer of dye or pigment on the upper substrate having a lightshielding film formed thereon, and forming a common electrode(ITO:Indium Tin Oxide) on an entire surface of the upper substrateinclusive of the color filter layer.

Referring to FIG. 6A, the process of fabricating a cell includesfabrication of the finished lower and upper substrates into a unit LCDcell state inclusive of the steps of alignment treatment for orientationof liquid crystal molecules (S11), sealing and spacing (S12), bonding ofthe upper and lower substrates (S13), scribing and breaking (S14),opening of the gate pad and/or data pad (S15), injection of liquidcrystal (S16), sealing liquid crystal injection opening (S17), andattachment of a polarizing plate (S18).

In more detail, the process of fabricating a cell includes the steps ofalignment treatment (S11) for forming and rubbing an alignment film foruniform orientation of liquid crystal molecules that enables regularliquid crystal driving and provides uniform display characteristics,sealing and spacing (S12) for scattering spacers and forming sealant formaintaining a fixed gap between the lower substrate of which TFTfabrication process is finished and the upper substrate of which colorfilter fabrication process is finished, bonding of the lower and uppersubstrates (S13), scribing and breaking (S14) for separating a pluralityof cells formed on the lower and upper substrates, opening of the gatepad and/or data pad (S15) for opening a gate pad and data pad of theseparated cell, injection of liquid crystal (S16) for injecting liquidcrystal between the cell by using capillary tube phenomenon and apressure difference, sealing liquid crystal injection opening (S17) forsealing the liquid crystal injection hole for blocking flow out of theliquid crystal from the cell having the liquid crystal injected therein,and attachment of a polarizing plate (S18) for attaching polarizingplates on both surfaces of the cell.

Referring to FIG. 6B, the step of opening of the gate pad and/or datapad (S15) may be carried out between the steps of sealing liquid crystalinjection opening (S17) and attachment of a polarizing plate (S18).Next, the step of fabricating a module is a process for fabricating acircuit portion for processing signals and connecting the LCD panel andthe circuit portion to fabricate a module. As described, the presentinvention suggests carrying out opening of the gate pad and the data padon the lower substrate during the cell fabrication process,particularly, after separating into cells by scribing and breaking, orsealing the liquid crystal injection hole. A method for fabricating anLCD panel of the present invention will be described for exemplaryembodiments.

FIG. 7 illustrates an enlarged plan view of a pixel on a TFT arraysubstrate in accordance with a first exemplary embodiment of the presentinvention, and FIGS. 8A-8C illustrate sections across lines IV-IV′,V-V′, and VI-VI′ in FIG. 7 showing the steps of a fabrication method.FIG. 9 illustrates a method for opening a gate pad in an LCD panel ofthe present invention, and FIGS. 10A and 10B illustrate before and afteropening of a gate pad in accordance with a first exemplary embodiment ofthe present invention. FIG. 11 illustrates a method for opening data padin an LCD in accordance with an exemplary embodiment of the presentinvention, and FIGS. 12A and 12B illustrate before and after opening ofa data pad in accordance with a first exemplary embodiment of thepresent invention. The first exemplary embodiment of the presentinvention suggests opening the gate pad and data pad in the cellfabrication process after fabrication of the lower substrate in an LCDusing five masks.

At first, referring to FIG. 8A, a conductive metal is deposited on atransparent lower substrate 80 and patterned, to form a gate pad 81 bhaving a large end of a predetermined area, a gate line 81 extended inone direction from the gate pad 81 b (see FIG. 7), and a gate electrode81 a projected from the gate line 81 in one direction. Next, aninsulating film 82, and first and second semiconductor layers (anamorphous silicon layer, and an n⁺ amorphous silicon layer) 83 and 84for forming the active layer, are deposited in succession on an entiresurface of the substrate having the gate electrode 81 a formed thereon.

Referring to FIG. 8B, a mask for forming the active layer is used inpatterning the first and second semiconductor layers 83 and 84 to formthe active layer 85 of an island form on the gate electrode 81 a.

Referring to FIG. 8C, a conductive metal is deposited on an entiresurface of the lower substrate 80 having the active layer 85 formedthereon and patterned, to form a data line arranged in one directioncrossing the gate line 81 having a data pad formed at one end thereof, asource electrode 86 a projected and extended from the data line to oneside direction of the gate electrode 81 a, and a drain electrode 86 bspaced a distance from the source electrode 86 a. In patterning theconductive metal, the active layer 85 of the semiconductor layer 84between the source electrode 86 a and the drain electrode 86 b areoveretched to form an ohmic contact layer 87. Then, a protection film 87is formed on an entire surface of the lower substrate 80 inclusive ofthe drain electrode 86 b. Thereafter, the protection film is etched toform a drain contact hole 88 (see FIG. 7) on the drain electrode 86 b.Next, a transparent conductive metal is deposited on the protection film87 having the drain contact hole 88 formed therein, and patterned toform a pixel electrode 89 in the pixel region so as to be in contactwith the drain contact hole 88. In this instance, since the pixelelectrode 89 is formed along the data line overlapped with apredetermined area of the data line 86, an aperture can be increased.After fabricating the lower substrate by the foregoing method, the stepsof alignment treatment (S11) for orientation of the liquid crystalmolecules, sealing and spacing (S12), bonding of the upper and lowersubstrates (S13), and scribing and breaking (S14) are carried out,thereby separating the lower substrate into cells. Thereafter, theopening of the gate pad 81 b and the data pad 86 c is carried out.

At first, referring to FIGS. 9, 10A, and 10B, an exposed portion of thegate pad 81 b of the liquid crystal cell is dipped in an insulating filmetchant 90 to remove the insulating film 82 and the protection film 87on the gate pad 81 b. States before and after opening the gate pad 81 bare shown in FIGS. 10A and 10B.

Next, referring to FIGS. 11, 12A and 12B, the data pad 86 c is opened bydipping an exposed portion of the data pad 86 c of the liquid crystalcell into an insulating film etchant 110 to remove the protection film87 on the data pad 86 c. States before and after opening the data pad 86c are shown in FIGS. 12A and 12B. Here, the upper substrate 100, theblack matrix layer 101, the common electrode 102, and the sealant 103are shown. The insulating film 82 and the protection film 87 are formedof silicon nitride SiNx and silicon oxide SiO₂ respectively. Sinceetchants for the materials give no damage to the sealant 103, an insideof the cell (i.e., an inside of the LCD panel) does not suffer fromdamage even if the gate pad and the data pad are dipped into theinsulating film etchant.

After opening the gate pad 81 b and the data pad 86 c, the steps ofinjecting liquid crystal into the cell (S16) by using capillary tubephenomenon and a pressure difference, sealing a liquid crystal injectionopening (S17) to seal the liquid crystal injection hole and block theliquid crystal from the cell having the liquid crystal injected therein,and for attaching polarizing plates on both surfaces of the cell (S18)are carried out. The foregoing opening of the gate pad 81 b and the datapad 86 c is carried out, not in the substrate fabrication process, butrather in the cell fabrication process, such as after separating cells,injecting the liquid crystal, and sealing the injection hole, as shownin FIG. 6B. Alternatively, the opening of the gate pad 81 b and the datapad 86 c may be made by an atmospheric plasma etching in which plasma isdirected to the gate pad 81 b and the data pad 86 c through a nozzle, orlaser etching in which the gate pad and the data pad are etched with alayer beam directly. Thus, the opening of the gate pad 81 b and the datapad 86 c is carried out after bonding the upper and lower substrates.

FIG. 13 illustrates an enlarged plan view of a pixel on a TFT arraysubstrate in accordance with a second exemplary embodiment of thepresent invention. FIGS. 14A-14D illustrate sections across linesIV-IV′, V-V′, and VI-VI′ in FIG. 13 showing the steps of a fabricationmethod. In the second exemplary embodiment of the present invention,four masks are used in fabrication of the lower substrate (the thin filmtransistor array substrate), of which fabrication method is as follows.

Referring to FIG. 14A, a gate metal layer is formed on the lowersubstrate 130 by deposition, such as sputtering, and patterned with afirst mask by photolithography and etching, thereby forming a gate line131 (see FIG. 13) in one direction. A gate electrode 131 a is formedprojected from one side of the gate line 131, and a gate pad 131 b isformed at one end of the gate line 131. The gate metal layer is a one ortwo layer of Cr, Mo, or Al.

Referring to FIG. 14B, a gate insulating film 132, an active layer 133,an ohmic contact layer 134 and data patterns are formed on the lowersubstrate 130 inclusive of the gate patterns (the gate line 131, thegate electrode 131 a, and the gate pad 131 b) in succession. A data pad136 is also formed in the data pad portion. In more detail, the gateinsulating film 132, the first and second semiconductor layers (anamorphous silicon layer and an n⁺ amorphous silicon layer) and a datametal layer are formed on the lower substrate 132 having the gatepatterns formed thereon in succession by deposition, such as PECVD, orsputtering. A photoresist pattern (not shown) is formed on the datametal layer with a second mask by photolithography. Here, using arefractive exposure mask having a refractive exposure portion at achannel portion of the thin film transistor as the second mask, thephotoresist pattern at the channel portion has a height lower than otherdata pattern portions. Then, wet etching is carried out using thephotoresist pattern to pattern the data metal layer and to form datapatterns including a data line 135, a source electrode 135 a, and adrain electrode 135 b integrated with the source electrode 135 a. Dryetching is carried out using the same photoresist pattern to pattern then⁺ amorphous silicon layer and the amorphous silicon layer at the sametime, thereby forming the ohmic contact layer 134 and the active layer133. After the photoresist pattern having a height relatively lower inthe channel portion is removed by ashing, the data pattern and the ohmiccontact layer 134 in the channel portion are etched by dry etching.Accordingly, the active layer 133 in the channel portion is exposed toseparate the source electrode 135 a and the drain electrode 135 b. Thephotoresist pattern left on the data pattern portion is stripped off. Inthe foregoing process, the photoresist pattern is also formed in thedata pad portion. The data pad 136 having the amorphous silicon layer,the n⁺ amorphous silicon layer, and the data metal layer stacked thereonis formed as the wet and dry etching are carried out. The gateinsulating film 132 is formed of an inorganic insulating material, suchas silicon oxide SiOx, or silicon nitride SiNx. The data metal layer isformed of Mo, Ti, Ta, or an Mo alloy.

Referring to FIG. 14C, a protection film 137 is formed on an entiresurface of the lower substrate 130 including the data line 135 bydeposition, such as PECVD or the like, and etched with a third mask byphotolithography and etching, thereby forming a contact hole 138. Thecontact hole 138 (see FIG. 13) is formed in the protection film 137 toexpose the drain electrode 135 b. The protection film 47 is formed of aninorganic insulating material, such as the same as the gate insulatingfilm 132, an acryl group organic compound of a low dielectric constant,or an organic insulating material (such as BCB or PFCB, or the like).

Referring to FIG. 14D, a transparent electrode material is deposited onan entire surface of the protection film 137 by deposition, such assputtering. Then, the transparent electrode material is patterned with afourth mask by photolithography and etching, thereby forming a pixelelectrode 139 in a pixel region. The pixel electrode 139 is electricallyconnected to the drain electrode 135 b through the contact hole 138. Thetransparent electrode is formed of Indium Tin Oxide (ITO), Tin Oxide(TO), or Indium Zinc Oxide (IZO). In this instance, by forming the pixelelectrode 139 along the data line 135, overlapped with a predeterminedarea of the data line 135, an aperture can be increased. Afterfabricating the lower substrate (the thin film transistor arraysubstrate) by the foregoing method, the steps of performing an alignmenttreatment (S11), sealing and spacing (S12), bonding of the upper andlower substrates (S13), and scribing and breaking (S14) are carried outto separate the lower substrate into cells. Thereafter, the opening ofthe gate pad 131 b and the data pad 136 c is carried out by dipping intoinsulating film etchant. Fabrication processes thereafter are similar tothese of the first exemplary embodiment. In this instance, as describedin the first exemplary embodiment, as an alternative to dipping intoetchant, the opening of the gate pad 131 b and the data pad 136 may bemade by an atmospheric plasma etching in which plasma is directed to thegate pad and the data pad through a nozzle, or laser etching in whichthe gate pad and the data pad are etched with a layer beam directly.

FIG. 15 illustrates an enlarged plan view of a pixel on a TFT arraysubstrate in accordance with a third exemplary embodiment of the presentinvention, and FIGS. 16A-16C illustrate sections across lines IV-IV′,V-V′, and VI-VI′ in FIG. 15 showing the steps of a fabrication method.

FIG. 17A illustrates a section showing the step of bonding a TFT arraysubstrate and a color filter array substrate of an LCD panel inaccordance with a third preferred embodiment of the present invention,and FIG. 17B illustrates a section showing the step of exposing a padportion in an LCD panel in accordance with a third exemplary embodimentof the present invention. In the third exemplary embodiment of thepresent invention, three masks are used in fabrication of the thin filmtransistor array substrate.

Referring to FIG. 16A, a gate metal layer is formed on the lowersubstrate 160 by deposition, such as sputtering, and patterned with afirst mask by photolithography and etching, to form a gate line 161 (seeFIG. 15) in one direction. A gate electrode 161 a is formed projectedfrom one side of the gate line 161, and a gate pad 161 b is formed atone end of the gate line 161. The gate metal layer is one or two layersof Cr, Mo, or Al.

Referring to FIG. 16B, a gate insulating film 162, an active layer 163,an ohmic contact layer 164, and data patterns are formed on the lowersubstrate 160 including the gate patterns (the gate line 161, the gateelectrode 161 a, and the gate pad 161 b) in succession. A data pad 166is also formed in the data pad portion. In more detail, the gateinsulating film 162, the first and second semiconductor layers (anamorphous silicon layer, and an n⁺ amorphous silicon layer), and a datametal layer are formed on the lower substrate 162 having the gatepatterns formed thereon in succession by deposition, such as PECVD, orsputtering. A photoresist pattern is formed on the data metal layer witha second mask by photolithography. In this instance, using a refractiveexposure mask having a refractive exposure portion at a channel portionof the thin film transistor as the second mask, the photoresist patternat the channel portion has a height lower than other data pattern parts.Then, wet etching is carried out using the photoresist pattern topattern the data metal layer, thereby forming data patterns including adata line 165, a source electrode 165 a, and a drain electrode 165 bintegrated with the source electrode 165 a. Next, dry etching is carriedout using the same photoresist pattern to simultaneously pattern the n⁺amorphous silicon layer and the amorphous silicon layer, thereby formingthe ohmic contact layer 164 and the active layer 163. After thephotoresist pattern having a height relatively lower in the channelportion is removed by ashing, and the data pattern and the ohmic contactlayer 164 in the channel portion are etched by dry etching. Accordingly,the active layer 163 in the channel portion is exposed to separate thesource electrode 165 a and the drain electrode 165 b. The photoresistpattern remaining on the data pattern portion is stripped off. In theforegoing process, the photoresist pattern is also formed in the datapad portion. The data pad 166 having the amorphous silicon layer, the n⁺amorphous silicon layer, and the data metal layer stacked thereon areformed as the wet and dry etching are carried out. The gate insulatingfilm 162 is formed of an inorganic insulating material, such as siliconoxide SiOx, or silicon nitride SiNx. The data metal layer is formed ofMo, Ti, Ta, or an Mo alloy.

Referring to FIG. 16C, a transparent pattern is formed with a thirdmask. In more detail, a transparent electrode material is formed on anentire surface of the gate insulating film 162 having the data patternsformed thereon by deposition, such as sputtering or the like. Then, thetransparent electrode material is patterned with a third mask byphotolithography and etching to form a pixel electrode 167 in the pixelregion. The pixel electrode 167 is overlapped and electrically connectedwith one side of the drain electrode 165 b. The transparent electrodemay be formed of Indium Tin Oxide (ITO), Tin Oxide (TO), or Indium ZincOxide (IZO). Next, a protection film 168 is formed on the TFT arraysubstrate. The protection film 47 is formed of an inorganic insulatingmaterial, such as SiNx and SiOx, an acryl group organic compound of alow dielectric constant, or an organic insulating material, such as BCBor PFCB, or the like.

Thereafter, referring to FIG. 17A, the TFT array substrate and the colorfilter array substrate are bonded. Before the bonding, a lower alignmentfilm 169 is coated on the protection film 168 of the TFT array substrateexcept the pad region, the gate pad portion, and the data pad portionpositioned therein. The lower substrate 160 and the upper substrate 170are bonded with sealant 175 to expose the pad region of the lowersubstrate 160. The color filter array substrate includes a black matrix171 on the upper substrate 170, a color filter 172 formed in each cellregion separated by the black matrix 171, and a common electrode 173 andan upper alignment film 174 stacked in succession on the black matrix171 and the color filter 172.

Next, referring to FIG. 17B, the protection film 168 and the gateinsulating film 162 in the pad region of the TFT array substrate areetched using the color array substrate as a mask. Accordingly, the gatepad 161 b and the data pad 166 are exposed. In the etching, dry etchingusing a laser beam, atmospheric plasma, or wet etching using dipping orspray may be used. The gate pad 161 b and the data pad 166 may beexposed using a similar process as that of the first embodiment.

Thus, the method for fabricating a TFT array substrate of the presentinvention can further simplify the fabrication process by employing athree mask fabrication process. However, in the etching of the gateinsulating film 162 and the protection film 168 to expose the gate pad161 b and the data pad 166, the lower substrate 160 or the gateinsulating film 162 is overetched, as shown in FIG. 18, thereby causingundercut of the gate pad 161 b and the data pad 166.

For preventing the undercut, a method for fabricating an LCD panel inaccordance with a fourth exemplary embodiment of the present inventionwill be described. In the fourth exemplary embodiment of the presentinvention, the TFT array substrate is fabricated using three masks. TheTFT array substrate before bonding of the upper and lower substrateswill be described.

Referring to FIGS. 19 and 20, the TFT array substrate includes gatelines 211 c and data lines 217 a arranged to cross each other with agate insulating film 214 in between, a thin film transistor T at everycross of the gate lines 211 c and the data lines 217 a, a pixelelectrode 225 a formed in each cell region formed by the cross, a gatepad 211 b formed at an end of the gate line 211, and a data pad 221formed at an end of the data line 217 a. The thin film transistor Tincludes a gate electrode 211 a projected from one side of the gate line211 c, a source electrode 217 b projected from one side of the data line217 a, a drain electrode 217 c connected to the pixel electrode 255 a,and an active layer 215 a overlapped with the gate electrode 211 a as achannel between the source electrode 217 b and the drain electrode 217c. The active layer 215 a is overlapped with the data pad 221, the dataline 217 a, the source electrode 217 b and the drain electrode 217 c,and further includes a channel region between the source electrode 217 band the drain electrode 217 c. An ohmic contact layer 216 a is formed onthe active layer 215 a for ohmic contact with the data pad 221, the dataline 217 a, the source electrode 217 b and the drain electrode 217 c.The thin film transistor T supplies a pixel voltage signal to the dataline 217 a in response to a gate signal supplied to the gate line 211 cto be charged to and stored in the pixel electrode 225 a. The pixelelectrode 225 a is connected to the drain electrode 217 c of the thinfilm transistor T. The pixel voltage of the pixel electrode 255 a causesa potential difference with the common electrode formed on the uppersubstrate (not shown). The potential difference rotates the liquidcrystal between the TFT substrate and the upper substrate by dielectricanisotropy to transmit the light incident thereto from a light source(not shown) through the pixel electrode 255 a toward the uppersubstrate.

The gate line 211 c is connected to a gate driver (not shown) throughthe gate pad part. The gate pad portion has a gate pad 211 b extendedfrom the gate line 211 c. On the gate pad 211 b, there are the gateinsulating film 214, an overetch protection pattern 220 partlyoverlapped with the gate pad 211 b, and a protection film 226 arestacked in succession. The data line 217 a is connected to a data driver(not shown) through the data pad portion. The data pad portion includesthe data pad 221 extended from the data line 217 a, and a data padprotection electrode 225 b for protection of the data pad 221. Betweenthe data pad 221 and the gate insulating film 214, there aresemiconductor patterns, i.e., the active layer 215 a, and the ohmiccontact layer 216 a.

A method for fabricating the foregoing TFT array substrate in an LCDpanel, and a method for fabricating an LCD panel having the TFT arraysubstrate will be described.

FIG. 19 illustrates a plan view of a TFT array substrate in an LCD panelin accordance with the fourth exemplary embodiment of the presentinvention, and FIG. 20 illustrates sections across lines VII-VII′,VIII-VIII′, and IX-IX′ in FIG. 19. FIGS. 21A-21G illustrate sectionsacross lines VII-VII′, VIII-VIII′, and IX-IX′ in FIG. 19 showing thesteps of a fabrication method. FIG. 22A illustrates a section showingthe step of bonding a TFT array substrate and a color filter arraysubstrate of an LCD panel in accordance with the fourth exemplaryembodiment of the present invention, and FIG. 22B illustrates a sectionshowing the step of exposing a pad portion in an LCD panel in accordancewith the fourth exemplary embodiment of the present invention.

Referring to FIGS. 21A and 21B, a gate pattern is formed on a lowersubstrate 210 by a first mask process. In detail, referring to FIG. 21A,a gate metal layer 211 is formed on the lower substrate 210 bydeposition, such as sputtering, and a photoresist is coated on the gatemetal layer 211, and patterned with a first mask 212 having atransmitting portion P1 and a shielding portion P2 by photolithographyto form a photoresist pattern 213. Referring to FIG. 21B, the gate metallayer 211 is etched using the photoresist pattern 213 to pattern thegate metal layer 211, thereby forming a gate line 211 a arranged in onedirection (see FIG. 19). A gate electrode 211 b is formed projected fromone side of the gate line 211 a, and gate patterns are formed includinga gate pad 211 b at an end of the gate line 211 a. The gate metal layeris one or two layers of Cr, Mo, or Al.

Referring to FIGS. 21C and 21E, a gate insulating film 214 is coated onan entire surface, and a semiconductor pattern and a gate pattern areformed thereon by a second mask process. In detail, referring to FIG.21C, a gate insulating film 214, a first semiconductor layer 215 of anamorphous silicon, a second semiconductor layer 216 of an n⁺ amorphoussilicon layer, and a data metal layer 217 are formed on the lowersubstrate 210 having the gate patterns successively formed thereon bydeposition, such as PECVD, and sputtering. The gate insulating film 214is formed of an inorganic insulating material, such as silicon oxideSiOx, or silicon nitride SiNx. The data metal layer is formed of Mo, Ti,Ta, or an Mo alloy. Then, photoresist is coated on an entire surface ofthe data metal layer 217 and subjected to photolithography using asecond mask 218 (i.e., a partial exposure mask) to form photoresistpatterns 219 a and 219 b. The second mask 218 has a transmitting portionP1, a shielding portion P2, and a partial transmitting portion P3 with arefractive exposure slit. The photolithography with the second mask 218removes the photoresist opposite to the transmitting portion P1 of thesecond mask 218 forms a first height d1 as the photoresist pattern 219 aopposite to the shielding portion P2 is not exposed, and forms a secondheight d2 at the photoresist pattern 219 b opposite to the partialtransmitting portion P3. Here, the photoresist pattern 219 opposite tothe channel portion of the thin film transistor is made to have a heightd2 lower than other data pattern part.

Referring to FIG. 21D, the data metal layer 217 is wet etched with thephotoresist pattern to pattern the data metal layer 217, thereby formingdata patterns including a data pad, an overetch prevention pattern, adata line 217 a, a source electrode 217 b, and a drain electrode 217 cintegrated with the source electrode 217 b. At the same time, anoveretch prevention pattern 220 is further formed to partly overlap withan outer portion of the gate pad 211 b but not overlaping with a centralportion of the gate pad 211 b so that the gate insulating film 214 isdisposed inbetween. Then, the photoresist pattern having a height d2relatively lower height in the channel portion is removed by ashing. Thedata pattern and the ohmic contact layer 216 a in the channel region areetched by dry etching to expose the active layer 215 a in the channelportion and to separate the source electrode 217 b and the drainelectrode 217 c. By the foregoing process, a data pad 221 having a stackof the first and second semiconductor layers and the data metal layer isformed at the end of the data line 217 a.

Referring to FIG. 21E, the photoresist pattern 219 a is removed bystripping. Referring to FIG. 21F, a transparent electrode material 222is deposited on an entire surface of the gate insulating film 214 havingthe data patterns formed thereon by deposition, such as sputtering, andphotoresist is coated on an entire surface of the transparent electrodematerial 222. Then, a photoresist pattern 224 is formed using a thirdmask 223 with a transmitting portion P1 and a shielding portion P2.Here, the photoresist exposed to a UV beam through the transmittingportion P1 is removed, and the photoresist not exposed due to theshielding portion P2 remains.

Referring to FIG. 21G, the transparent electrode material 222 ispatterned by etching using the photoresist pattern 223 as a mask,thereby forming a pixel electrode 225 a and a data pad protectionelectrode 225 b such that the pixel electrode 225 a is electricallyconnected to the drain electrode 217 c, and the data pad protectionelectrode 225 b has a width larger than the data pad 221. Thetransparent electrode may be formed of Indium Tin Oxide (ITO), Tin Oxide(TO), or Indium Zinc Oxide (IZO). Then, a protection film 226 is coatedon the lower substrate 210 having the pixel electrode 225 a formedthereon. The protection film 226 is formed of an inorganic insulatingmaterial, such as SiNx or SiOx, an acryl group organic compound of a lowdielectric constant, or an organic insulating material, such as BCB orPFCB, or the like.

Referring to FIG. 22A, the TFT array substrate and the color filterarray substrate are bonded with a sealant 235. Before the bonding, alower alignment film 227 is coated on the protection film 226 of the TFTarray substrate excluding a pad region having the gate pad portion andthe data pad portion positioned therein. The color filter arraysubstrate includes a black matrix 231, a color filter 232 in each cellregion separated by the black matrix 231, a common electrode 233, and anupper alignment film 234 stacked in succession on the black matrix 231and the color filter 232. Accordingly, the pad region including the gateportion and the data pad portion is exposed.

Then, referring to FIG. 22B, the protection film 226 and the overetchprevention pattern 220 in the pad region are entirely removed by a padopening using the color filter substrate as a mask, and a gate hole 240is formed in a gate insulating film 214 to overlap with the gate pad 211b. Alternatively, it should be recognized that the overetch preventionpattern 220 need not be removed and can remain. The pad opening exposesthe gate pad 211 b and the data pad protection electrode 225 b. As theprotection film 226 is removed at the pad opening, the data pad terminal225 b and the gate insulating film 214 in the vicinity of the data padterminal 225 b are exposed. Similarly, the gate pad 221 b, as theprotection film 226 and the overetch prevention pattern 220 are removed,and the gate hole 240 is formed in the gate insulating film 214, thegate pad 211 b is exposed.

Since the overetch prevention pattern 220 is formed overlapped with anouter portion of the gate so that the gate insulating film 214 isdisposed inbetween, a thickness ‘d’ of the overetch prevention pattern220 and the protection film 226 stacked on the outer portion of the gatepad 211 b is thicker than a height of the gate insulating film 214 andthe protection film 214 stacked on a central portion of the gate pad 211b. For an example, if a height of the gate insulating film 214 and theprotection film 226 is 4000-6000 Å (Angstroms), a height of the overetchprevention pattern 220 and the protection film 226 is 7000-9000 Å(Angstroms). Accordingly, in the pad opening, only the protection film226 and the overetch prevention pattern 220 are removed from the outerportion of the gate pad 211 b, thereby leaving the gate insulating film214. Thus, since the gate pad portion has the gate insulating film 214left at the outer portion thereof, and the data pad portion has the datapad protection electrode 225 b protecting the data pad, the undercut inthe pad opening can be prevented.

As has been described, the method for fabricating an LCD panel of thepresent invention has the following advantage. First, the carrying outof the gate pad and data pad opening, not during fabrication of thelower substrate, but after bonding of the upper and lower substratespermits simplification of a lower substrate fabrication process. Second,the opening of the gate pad and the data pad by dipping in an etchantafter bonding the upper and lower substrates permits to preventdefective opening of the gate pad or the data pad. Third, the formationof the overetch prevention pattern overlapped with the gate insulatingfilm at an outer portion of the gate pad and the formation of the datapad protection electrode on the data pad prevents undercut in the padopening.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the method for fabricating aliquid crystal display panel of the present invention without departingfrom the spirit or scope of the invention. Thus, it is intended that thepresent invention cover the modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalents.

1. A method for fabricating a liquid crystal display panel, comprisingthe steps of: forming a thin film transistor array substrate including:a screen region having gate lines, data lines, thin film transistors,and pixel electrodes, a pad region having gate pads, an overetchprevention pattern formed overlapped with a gate insulating film in anouter portion of each gate pad, and data pads, data pad protectionelectrodes each on a respective data pad, and a protection film on anentire surface of the screen region and the pad region; forming a colorfilter array substrate; bonding the thin film transistor array substrateand the color filter array substrate so that the pad region remainsuncovered; etching a portion of the protection film and the overetchprevention pattern of the pad region to partially expose the gate padsand the data pad protection electrodes, and to form gate holes in thegate insulating film over corresponding gate pads.
 2. The methodaccording to claim 1, wherein the step of forming a thin film transistorarray substrate includes the steps of: forming the gate lines, gateelectrodes each projected from a side of a respective gate line, and thegate pads each at an end of a respective gate line on a substrate usinga first mask process; forming a gate insulating film on the substratehaving the gate lines, the gate electrodes, and the gate pads; formingthe data lines crossing the gate lines, source electrodes of the thinfilm transistors each projected from a side of a respective data line,drain electrodes each spaced from a respective source electrode, a datapattern having the data pads each at an end of a respective data line, asemiconductor pattern formed under the data pattern to form respectivechannel portions between the source electrodes and the drain electrodes,and an overetch protection pattern at an outer portion of the gate padsto overlap with the gate insulating film, using a second mask process;forming a transparent electrode pattern having the pixel electrodes andthe data pads using a third mask; and forming a protection film on thesubstrate including the transparent electrode pattern.
 3. The methodaccording to in claim 2, wherein the overetch prevention patternincludes a semiconductor pattern and the data pattern overlappedthereon.
 4. The method according to claim 2, wherein the data padprotection electrodes are each formed having a width greater than awidth of each of the data pads.
 5. The method according to claim 1,wherein the step of forming the color filter array substrate includesthe steps of: forming a black matrix layer; forming a color filter ineach cell region separated by the black matrix layer; forming a commonelectrode on the black matrix layer and the color filter; and forming anupper alignment film on the common electrode.
 6. The method according toclaim 1, wherein the step of forming a thin film transistor arraysubstrate further includes the step of coating a lower alignment film onthe substrate excluding the pad region.
 7. The method according to claim1, wherein the step of forming a thin film transistor array includes thesteps of: forming the gate line, the gate pad at one end of the gateline, and a gate electrode projected from a side of the gate line on thelower substrate using a first mask; forming an insulating film on asurface of the lower substrate having the gate line, the gate pad, andthe gate electrode; forming an active layer having an island shape onthe insulating film over the gate electrode using a second mask; formingthe data line to cross the gate line, the data pad at an end of the dataline, a source electrode projected from the data line in a directiontoward the gate electrode, and a drain electrode spaced a distance fromthe source electrode using a third mask, a pixel region being defined bythe crossed data line and gate line; forming the pixel electrode in thepixel region to contact the drain electrode using a fourth mask; andforming a protection film on a surface of the lower substrate having theinsulating film, the active layer, the data line, the data pad, thesource electrode, and the drain electrode.
 8. The method according toclaim 7, wherein the overetch prevention pattern includes asemiconductor pattern and the data pattern overlapped thereon.
 9. Themethod according to claim 7, wherein the data pad protection electrodesare each formed having a width greater than a width of each of the datapads.